Liquid chromatography apparatuses have recently come to be frequently used as methods for analyzing samples in the fields of organic chemistry, biochemistry, medicine and the like. FIG. 14 shows an example of a conventional liquid chromatography apparatus (see, for example, Patent Document 1). A liquid chromatography apparatus X shown in this drawing is provided with a sample preparation unit 91, a flow path directional valve 92, a manifold 93, a feed pump 94, an analysis unit 95 and a controller 96. The sample preparation unit 91 produces a sample by diluting a sample S such as blood with a diluent Ld. A fixed amount of this sample is accumulated in an injection loop 92b of the flow path directional valve 92. When a six-way valve 92a of the flow path directional valve 92 rotates, for example, from the state shown in the drawing, the fixed amount of sample is delivered to the analysis unit 95. The analysis unit 95 has a pre-filter 95a, a column 95b and a photometric unit 95c. After a fixed amount of sample has been adsorbed by a filler of the column 95b, an eluent La is fed from the manifold 93 by the feed pump 94. This eluent La is supplied to the column 95b through the flow path directional valve 92. After having been adsorbed by the filler, the sample is desorbed by the eluent La and separated into each component within the column 95b. The photometric unit 95c is able to analyze each separated component by, for example, measuring absorbance. The controller 96 controls driving of the sample preparation unit 91, the flow path directional valve 92, the manifold 93 and the analysis unit 95.
In the analysis described above as well, other components in addition to the analysis targets remain in the column 95b. An eluent Lb is supplied from the manifold 93 to the column 95b through the flow path directional valve 92 for the purpose of washing away these other components. An eluent having, for example, a higher salt concentration than the eluent La is used for the eluent Lb. Subsequently, it is necessary to return the salt concentration of the system, including the column 95b, to that of the eluent La in order to resume the above-mentioned analysis. An eluent Lc is supplied from the manifold 93 to the column 95b through the flow path directional valve 92 in order to adjust the salt concentration. An eluent having a lower salt concentration than the eluents La and Lb is used for the eluent Lc. As a result, the salt concentration that was increased as a result of supplying the eluent Lb is lowered. The salt concentration of the column 95b can subsequently be made to be a salt concentration suitable for analysis by again supplying the eluent La.
However, hysteresis of a salt concentration Ds of the column 95b to which is sequentially supplied the eluents La, Lb and Lc is shown in FIG. 15. Namely, in the column 95b, the eluent is respectively switched from the eluent La to the eluent Lb at a time T1, from the eluent Lb to the eluent Lc at a time T2, and from the eluent Lc to the eluent La at a time T3. This switching of the eluents La, Lb and Lc is carried out by the manifold 93. Mutual mixing of the eluents La, Lb and Lc cannot be avoided during the switching operation of the manifold 93. The salt concentrations are unable to be switched instantaneously at the times T1, T2 and T3 due to the resulting turbidity, causing the hysteresis to change gradually. As a result, a considerable amount of time was required until the salt concentration of the column 95b returned to a concentration suitable for analysis. In addition, a considerable amount of eluent was consumed until the salt concentration returned to the concentration of each eluent.
Patent Document 1: Japanese Patent Application Laid-open No. 2007-240500